I would suspect by the shape and design that itís a Signalling lamp, its not a model that Iím familiar with, however it looks very similar to the USN models of world war two, as used for ship to ship communications in Morse code.
"Now, I've designed this like a collapsing bag ! "
I think your right,I was thinking airplane morse lamp.
on it is the letters S.N Thomson Ohio,sow its US made
It is a civilian style search light IMO check out this link for a field version........Redirect Notice.....................
[h=3]e plu∑ri∑bus u∑num[/h]
Look at my post for "Japanese Pistol Grip Switch." Could be a similar use. I would guess a signalling lamp, too. Why else have a lamp with a momentary contact rather than a toggle on-off.